#!/usr/bin/perl

use strict;
use warnings;

my %foo;

$foo{bar} = "key bar's value";

if(exists($foo{qux})) {
    print "\$foo{qux} exists";
}

if(exists($foo{bar}) && exists($foo{bar}{baz})) {
    print "\$foo{bar}{baz} exists\n";
}

if(exists($foo{bar})) {
    print "\$foo{bar} popped into existence\n";
}